[clang] [LifetimeSafety] Detect use of a reference type as a use of underlying origin (PR #184295)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-analysis

Author: Zhijie Wang (aeft)

<details>
<summary>Changes</summary>

Writing through a reference (e.g., `ref = 10`) does not rebind the reference, so it should not kill the liveness of its underlying origin.

Fixes #<!-- -->180187

---
Full diff: https://github.com/llvm/llvm-project/pull/184295.diff


2 Files Affected:

- (modified) clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp (+2-1) 
- (modified) clang/test/Sema/warn-lifetime-safety-invalidations.cpp (+3-5) 


``````````diff
diff --git a/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp b/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp
index f39d677758393..6325e63b2388b 100644
--- a/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp
+++ b/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp
@@ -347,7 +347,8 @@ void FactsGenerator::handleAssignment(const Expr *LHSExpr,
   // assigned.
   RHSList = getRValueOrigins(RHSExpr, RHSList);
 
-  if (const auto *DRE_LHS = dyn_cast<DeclRefExpr>(LHSExpr))
+  if (const auto *DRE_LHS = dyn_cast<DeclRefExpr>(LHSExpr);
+      DRE_LHS && !DRE_LHS->getDecl()->getType()->isReferenceType())
     markUseAsWrite(DRE_LHS);
   // Kill the old loans of the destination origin and flow the new loans
   // from the source origin.
diff --git a/clang/test/Sema/warn-lifetime-safety-invalidations.cpp b/clang/test/Sema/warn-lifetime-safety-invalidations.cpp
index 65d676cbe8361..60a6be9f0c2a7 100644
--- a/clang/test/Sema/warn-lifetime-safety-invalidations.cpp
+++ b/clang/test/Sema/warn-lifetime-safety-invalidations.cpp
@@ -259,11 +259,9 @@ namespace ElementReferences {
 
 void ReferenceToVectorElement() {
   std::vector<int> v = {1, 2, 3};
-  int& ref = v[0];
-  v.push_back(4);
-  // FIXME: Detect this as a use of 'ref'.
-  // https://github.com/llvm/llvm-project/issues/180187
-  ref = 10;
+  int& ref = v[0]; // expected-warning {{object whose reference is captured is later invalidated}}
+  v.push_back(4);  // expected-note {{invalidated here}}
+  ref = 10;        // expected-note {{later used here}}
   (void)ref;
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/184295